This invention concerns a system for identification and determination of a multiple number of moving bodies at a given point on their path.
Such systems enable automatic timing of sports events like automobile races, for example. They generally include a mobile device mounted on each moving body. Each mobile device includes a transmitter capable of emitting a characteristic radio identification signal from the moving body. A fixed receiving antenna is set up in proximity to the said given point and designed to receive the different identification signals, and means are provided for processing the identification signals received by the receiving antenna to determine for each signal the identity of the moving body which emitted it and the moment of its passage by the receiving antenna.
In the systems known to date, as, for example, in the one described in British Pat. No. 1,517,173, the mobile transmitter contains a multivibrator or a quartz oscillator tuned to a frequency characteristic of the moving body which carries it, and it permanently emits the identification signal of the moving body. The receiving antenna is usually set up on the ground across the path of the moving bodies.
These systems have a number of disadvantages, including that of requiring high electric power consumption by the carried devices. Consequently, these devices, which must contain their own power supply, are difficult to miniaturize and it is necessary to provide devices and procedures for turning them off whenever the moving bodies are not being timed. In the case of automobile races, for example, the timing crews must constantly intervene, for example, between different trial meets, in order to switch the different transmitters on and off. This imposes a burden on the crews, and, when an error occurs, the power source of one transmitter or another will be discharged or transmitters may even be disconnected at the starting time of the race.
Another difficulty associated with operating the transmitters continuously over the entire path of the moving bodies, which often exceeds several kilometers is the radio enroachment that such a system can make in the vicinity of the course where the trial to be timed is run. The extent of that enroachment, combined with the strict regulations relating to the use of radio frequencies, results in limiting the possibilities of using known systems.
Other disadvantages are due to the nature of the transmitters used on the moving bodies. Electronic multivibrator circuits are difficult to stabilize under the harsh conditions which might prevail, notably, during automobile races. The use of quartz oscillators has also been developed, but the fragility of these devices has led to numerous failures, notably, in case of shock.
Furthermore, as long as the sole characteristic of the identification signals consists of their frequency, their detection by the means of processing these signals in an environment that generally creates interference is difficult. That fact usually leads to increasing the transmitter power or using complex antennas, formed, for example, by a combination of antennas, as described in U.S. Pat. No. 4,274,076.
U.S. Pat. No. 3,546,696 previously described a system in which the moving bodies are equipped with mobile devices containing a receiver which triggers the emission of an identification signal the moment it receives a control signal emitted by a fixed transmitter set up below the finish line. However, the moment of passage is defined by the exact instant of tripping, which implies an absolutely directional fixed transmitting antenna and low-level transmission to prevent a premature tripping of mobile transmitters. This results in difficulties in setting up the antenna and in an increased risk of error in timing likely to be caused by an accidental tripping of a mobile transmitter due to interference. Furthermore, the transmitters described are each equipped with a quartz oscillator and an audio frequency oscillating circuit to produce the identification signal, and the problems involved in such systems has already been described.
An object of this invention is to provide a system which solves the above-mentioned problems, by making it possible to reduce substantially the power consumption of the mobile devices as well as the extent of radio encroachment of the system, allowing the elimination of quartz oscillators and offering new possibilities of detection of identification signals without complicating the structure of the antenna placed on the finish line.
The invention provides several advantages including the possibility of easily selecting for the different mobile devices of identical design the characteristic frequency of their identification signals and of very precisely determining the moment of passage of the moving body by the receiving antenna. Furthermore, the system according to the invention may very easily be used for transferring different information from the moving bodies to the receiving antenna or vice versa.
These objects and advantages are attained by providing for the control signal to be emitted by the fixed transmitter in a limited portion of the space situated in front of and past the line. In addition, each mobile device includes means for operating the transmitter it contains as long as its receiver receives the control signal. In that way, the identification signal is emitted throughout the duration of passage of the moving body past the line, and means of processing that signal can use variations of intensity or of frequency for determining in a very precise manner, unassociated with the directivity of the antenna, the exact moment of passage over the line.
The identification signal is produced directly from the control signal, so that a phase relationship exists between these different signals, which an be advantageous to the means of for processing the identification signals.